Having done both I would recommend Charter. More fun, you get to see more places (albeit they may not be exactly tourist quality) and once you get onto a proper charter mob (not just laps around the bungles/ wackadoo) then the cleaning of aircraft becomes a once a week thing with a quick vacuum after each flight. You will end up on larger faster aircraft within a year and twins shortly after that. Yes the hours (Working, not flight) are no where near as good as instructing, however if you want to build night hours then you have to fly at night. If you want to build IF time then you have to fly when the weather is a poor.
I found that charter work made me far more independent as a pilot than instructing. As an instructor you tend not to drift to far from known routes and training areas, most of the problems you encounter you can ask your CFI about and pick up advise, with charter you have to make all the calls yourself, often with only cursory advise from the ever busy CP.
I also found that charter enabled better connections in the industry, you may run into a fellow pilot out in the middle of nowhere who informs you of a twin job up for grabs, or you help out a stranded pilot only to run into them 4 years later at your airline interview.
Yes charter was harder then instructing, but it was worth the extra effort. Yes it often included VERY early starts with late finishes but that's how you fit an 8+hr flying day in.
